A group of conservative activists huddled behind closed doors Thursday at a Washington hotel to plot strategy to stop Republican front-runner Donald Trump, including calling for a unity ticket to oppose him and a floor fight at the GOP convention to deny him the nomination.

The meeting was led by conservative talk radio host Erick Erickson, a longtime outspoken critic of Mr. Trump.

“We believe that the issue of Donald Trump is greater than an issue of party. It is an issue of morals and character that all Americans, not just those of us in the conservative movement, must confront,” the group said in a statement posted on Mr. Erickson’s website.

The only member of the group identified was Mr. Erickson. The other attendees were described as “grass-roots conservative activists from across the country.”

The meeting underscored the increasing dismay within the Republican establishment as Mr. Trump moves closer to capturing the nomination, either by winning the requisite 1,237 delegates or at a brokered convention in July in Cleveland.

“We call for a unity ticket that unites the Republican Party. If that unity ticket is unable to get 1,237 delegates prior to the convention, we recognize that it took Abraham Lincoln three ballots at the Republican convention in 1860 to become the party’s nominee and if it is good enough for Lincoln, that process should be good enough for all the candidates without threats of riots,” the statement said.

“We encourage all former Republican candidates not currently supporting Trump to unite against him and encourage all candidates to hold their delegates on the first ballot,” it continued. “Lastly, we intend to keep our options open as to other avenues to oppose Donald Trump. Our multiple decades of work in the conservative movement for free markets, limited government, national defense, religious liberty, life, and marriage are about ideas, not necessarily parties.”